Antiproliferative effects of 1,25-dihydroxyvitamin D and its analogues have been demonstrated in tissue culture and animal models of many different human cancers. Intermittent exposure to 1,25-dihydroxyvitamin D suppresses neoplastic cell growth in vitro and maybe sufficient to achieve antiproliferative effects in vivo. Toxicity of Vitamin D in humans, principally hypercalcemia, increases with duration of exposure to vitamin D. The hypothesis of they study is that intermittent dosing may produce antiproliferative levels of 1,25-disydroxyvitamin D while minimizing toxicity. Such intermittent dosing has not been studied and maximally tolerated doses of 1,25-dihydroxyvitamin D given intermittently have not been defined. We seek to define the maximally tolerated dose and optimal treatment schedule of Calcitriol delivered intermittently.